Non_Iv_Contrast_in_Ct

“Contrast medium is a substance that is radio opaque when exposed to x-rays. The administration of such a compound allows for examination by a radiologist of the tissue or organ being filled” Contrast media is used to help improve visualization of normal and abnormal structures. “the degree of enhancement is related to the method of contrast administration and the dose and concentration of contrast received as well as the delay between contrast administration and image acquisition” Since 1895 when x-rays were first discovered contrast media has progressed in development through history. In 1896 the first contrast study was performed as a intravenous urography. In 1920 the 1st iodinated contrast medium was used. During the 1950 and 60’s low toxicity and non ionic contrast medium was produced. Today contrast media is a highly developed and routinely used medium. Contrast media can be divided into two types positive and negative. Positive contrast media have a higher attenuation properties in comparison to the body’s tissues and thus show up as white/ grey on an image. Example of positive are barium and iodine. Negative contrast agents have lower attenuation properties in comparison to the body’s soft tissue and thus show up as dark/ grey on an image. Examples of negative contrast agents are air, oxygen, water and milk. The administration of non-intravenous contrast media in CT can be performed by having the patient take it orally, by performing it rectally by way of an enema, or by inhalation. Patient preparation is usually required when studies of the GI tract and abdominal organs are requested using contrast media. It is important to eliminate as much food as possible from the stomach and intestines in order to help the sensitivity of the CT exam using contrast. Food and food remains can mimic disease when the contrast is present so a fleet kit may be required to cleanse the colon the night before or over a couple of days prior to the exam. Also a regimen of not eating or drinking several hours before the CT exam may also be required. The preparation time will vary depending on the exam being performed and departmental protocol. ORAL: Oral contrast in CT is often used to enhance CT images of the abdomen and pelvis, highlighting the structures of the gastrointestinal system. There are two main types of substances used for oral CT contrast. Barium sulphate is the most common oral contrast agent used in CT. The second type of contrast agent is used as a substitute for barium and is called Gastrografin. Barium contrast looks like and has a similar consistency as a milk shake. It is mixed with water and depending on the brand used, may have different flavours. Gastrografin contrast is a water-based drink mixed with iodine and has a tinted yellow color. Patients usually need to drink at least 1000 to 1500 cc (about three to four 12 oz. drinks) to sufficiently fill the stomach and intestines with oral contrast. Rectal contrast is often used to enhance CT images of the large bowel, rectum and other organs in the pelvis. The same two types of contrast media used for oral administration of CT contrast, Barium and Gastrografin, are also used for rectal administration of contrast but in different concentrations. Rectal CT contrast is usually administered using an enema where a small plastic tip is inserted into the rectum while a patient lies on their side. This tip is connected to a bag filled with the barium or gastrografin contrast through a tube. After the tip is inserted, the patient lies flat and the bag is raised above head level to allow the contrast to fill the lower intestines. During this filling phase, the patient may feel mild discomfort, coolness, and generalized fullness. The rectal contrast helps to increase the sensitivity of the CT exam by outlining not only the large intestines (colon), but also the bladder, the uterus in female patients and other organs. After the exam is complete, the rectal contrast will be drained and the patient may go to the bathroom. A much less common type of contrast used in CT is inhaled as a gas and used for special lung and brain imaging. This technique is called Xenon CT and is only available at a small number of locations throughout the world and is only performed for rare cases. Xenon CT is used for special highly sharp imaging of the lung, the brain and other parenchymal organs. In Xenon CT of the brain, the process involves dynamic scanning in conjunction with inhalation of a mixture of 28% xenon gas and oxygen as a contrast agent. This is performed for several minutes via a face mask. Once inhaled, the gas is absorbed by the lungs into the blood which then goes on to diffuse through the blood brain barrier to enter the brain parenchyma. Scans are made prior to inhalation, during inhalation time and may be acquired following inhalation. Barium Sulphate, more commonly known as Barium, is a non-intravenous contrast agent commonly used in computed tomography to enhance the contrast in the GI tract. It is a metallic element that is chemically similar to calcium, but more reactive. It is a common, naturally occurring mineral. The most typical form of administration for barium in CT is orally, but it can also be administered rectally for some examinations of the large bowel and rectum. This white or yellowish insoluble powder is mixed with water to make a thick, chalky suspension to produce the contrast agent. Some sweeteners and flavorings can also added to the mixture in an attempt to make it more palatable, often with no avail. Barium presents as a radio-opaque substance in the stomach, small bowel, large bowel and rectum in a CT of the abdomen and pelvis. This occurs as a result of the relatively high atomic number of barium (Z=56), which means that it will attenuate the x-ray beam more than that of the surrounding tissues. This then allows these regions of the GI tract to be easily identified and highlighted in the CT, which is critical in its proper interpretation. There are some possible side effects associated with the ingestion of a barium sulphate suspension which should also be mentioned. These include nausea, vomiting, diarrhea and headaches. In most cases, it is considered that the benefits of consuming the barium far out-weigh the risk of these possible side effects, although, with certain medical conditions such as perforations, peptic ulcers, or any acute conditions that may require surgery, use of an alternative to barium, such as Gastrografin or Ultravist, is recommended. Diatrizoic acid, better known as Gastrografin, is a water-soluble iodine based contrast agent that is used non-intravenously in CT. Similarly to barium, gastrografin can be administered both orally and rectally, depending on the examination. It may be used as an alternative to barium sulphate in CT for use in patients who are allergic to barium, in cases where the barium might leak into the abdominal cavity, and when other contraindications are present. Gastrografin is a radiopaque contrast medium that is used to coat the inner lumen of the GI tract. The relatively high atomic weight of the iodine in the contrast contributes sufficient radiodensity for radiographic contrast with the surrounding tissues. This highlights the anatomy of the GI tract in the scan to allow it to be easily identified. Like Barium, Gastrografin has some associated side effects with its use. These include diarrhea, nausea, vomiting, mild swelling, itching and existing inflammations of the bowel may temporarily worsen. It should also be noted that due to the iodine content of Gastrografin, patients with a history of sensitivity to iodine should avoid its use, as allergic and anaphylactic reactions may occur. Its use should also be avoided in pediatrics and dehydrated patients. A form of non IV contrast used is an iodinated contrast medium, such as Iopromide, or commonly known under its marketing name Ultravist. This is a water-soluble iodinated contrast enhancement agent utilised in intravascular examinations such as CT pulmonary angiograms and also in CT brain scans. It is non-ionic, meaning the iodine content is bound in an organic compound, as well as low osmolality characteristics, which tends to decrease the chance of side-effects. While Ultravist is regularly used as an intravenous contrast, it is also used in joint injections in CT athrograms, to help visualize the joint cavity and any surrounding pathology, or used in CT scans where a patient is query aspiration instead the use of barium, to ensure barium isn’t aspirated into the lung. The predominant contraindication for the use of Ultravist is with patients with a known hypersensitivity or previous reaction to any iodinated contrast. Xenon is a noble gas, with an atomic number of 54 which is relatively high compared to that of air and surrounding tissue, and therefore contributes to contrast enhancement and can be utilised as a contrast medium. This is done so via inhalation mixed with oxygen, at which point it then diffuses into the blood. It can be used in examinations that require visualizing and measuring cerebral blood flow throughout various regions of the brain, as cerebral blood flow will be of a higher density, which will give greater image contrast on a Xenon-enhanced Brain CT scan. Usually there are three scans, including pre-inhalation, during inhalation, and post inhalation in evaluating cerebral blood flow. Xenon can also be used in specialised imaging of the lungs, to evaluate pulmonary function and air flow into the lungs, as well as in a CT myelogram, which again uses the contrast properties of xenon gas to image the spinal canal and its contents. Xenon gas is not a radioactive gas, therefore the only radiation is coming from only the CT scan itself. However excessive inhalation of xenon can have side-effects, as it is a narcotic gas as well as an anesthetic in large amounts. In our presentation we have decided to include a case study that we came across during our study of non IV contrast. The case study shows how non IV contrast can be useful in diagnoses of pathology and the advantage that it poses over general CT and other imaging modalities. This case study involves the administration of per rectal contrast The history of this patient was a 37 year old male who presented to the emergency department with severe lower abdominal pain, a fever, air in their urine during micturation and mucousal diarrhoea. 2 months prior the patient was treated in the urology department for a urinary tract infection that was treated with antibiotics. The patient had no history of chronic illness and or any family members with similar complaints. Upon physical examination, there was a tender area located suprapubically. To assess this indication the patient underwent ultrasound, MRI and CT examinations. The pelvic ultrasound revealed a thickened and inflamed sigmoid colon and an air-filled tract extending from the sigmoid. The pelvic MRI revealed a fistula between the bladder and sigmoid colon but was inconclusive in terms of the pnematuria so a CT with per-rectal contrast was planned. The CT scan, as seen, revealed inflammation and thickening of an 18cm portion of the sigmoid colon. It was also noted that there were many diverticuli along the wall of the sigmoid colon. The fistula noted in the MRI scan was also visible in the CT scan and pericolic inflammation was also seen. A colonoscopy was then performed and tested the diverticuli in the sigmoid colon for malignancy but the results were negative. Biopsies revealed that the patient was suffering from divertivculitis compounded with sigmoidovesical fistula that was visible on the MRI and the CT scan. After diagnosis the inflamed portion of the sigmoid colon suffering from diverticulitis was surgically removed and the fistula was repaired. Through the use of the barium enema a conclusive diagnosis was made. 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